The present invention relates to rollers or analogous devices for the treatment of fibrous materials with the application of heat and/or solvents. More particularly, the invention relates to improvements in rotary devices which can be used to reinforce or strengthen selected portions of layers, webs, sheets or panels of nonwoven fibrous material as a result of controlled and oriented application of heat and/or suitable solvents.
It is already known to heat-treat or solvent-treat layers of fibrous material with rollers of the type having protrusions which extend outwardly from the peripheral surface of a cylindrical body. The protrusions may be in the form of ribs or in the form of discrete protuberances of relatively small width and length, as considered in the circumferential and axial directions of the cylindrical body. It is also known to impart to the protrusions a substantially frustoconical configuration so that the protrusions taper in directions away from the peripheral surface of the cylindrical body. In other words, the cross-sectional area of the base of each protrusion in the region of the peripheral surface is larger than the cross-sectional areas which are more distant from the peripheral surface. Rollers of the above outlined character are often used to enhance the absorbency of layers of fibrous material which can be used as absorbent pieces of textile material or the like. As a rule, the taper of such protrusions is quite pronounced so that each protrusion resembles a strongly tapering pyramid or a similar geometric body. This is intended to reduce the likelihood of development of undercuts during the engraving of a cylindrical body for the purpose of making protrusions thereon. However, such formation of protrusions also brings about serious drawbacks, for example, because the fibers are likely to be bonded to each other in those regions which are adjacent to the facets or flanks of the protrusions, i.e., not only in the regions of the tips or outermost portions of such protrusions. Moreover, the useful life of such conventional rollers is relatively short because the protrusions cannot be ground a large number of times since each grinding entails a pronounced increase in the areas of top lands of the protrusions with attendant much more pronounced transfer of heat between the tips of the protrusions and the adjacent fibers. Still further, repeated grinding of the protrusions entails a pronounced reduction of the volume of the grooves between neighboring protrusions so that such grooves can accommodate a smaller number of fibers when the rollers of the just described conventional character are in actual use.